This invention relates generally to inflatable restraint systems and, more particularly, to the generation of inflation gas used in such systems.
It is well known to protect a vehicle occupant by means of safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., xe2x80x9cpassive restraint systems.xe2x80x9d Such systems commonly contain or include an inflatable vehicle occupant restraint or element, such as in the form of a cushion or bag, commonly referred to as an xe2x80x9cairbag cushion.xe2x80x9d In practice, such airbag cushions are typically designed to inflate or expand with gas when the vehicle encounters a sudden deceleration, such as in the event of a collision. Such airbag cushions may desirably deploy into one or more locations within the vehicle between the occupant and certain parts of the vehicle interior, such as the doors, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such parts of the vehicle interior.
Various types or forms of such passive restraint assemblies have been developed or tailored to provide desired vehicle occupant protection such as based on either or both the position or placement of the occupant within the vehicle and the direction or nature of the vehicle collision, for example. In particular, driver side and passenger side inflatable restraint installations have found wide usage for providing protection to drivers and front seat passengers, respectively, in the event of head-on types of vehicular collisions. Further, side impact inflatable restraint installations have been developed to provide improved occupant protection against vehicular impacts inflicted or imposed from directions other than head-on, i.e., xe2x80x9cside impacts.xe2x80x9d
In addition to an airbag cushion, inflatable passive restraint system installations also typically include a gas generator, also commonly referred to as an xe2x80x9cinflator.xe2x80x9d Upon actuation, such an inflator device desirably serves to provide an inflation fluid, typically in the form of a gas, used to inflate an associated airbag cushion. Many types or forms of inflator devices have been disclosed in the art for use in inflating an inflatable restraint system airbag cushion.
xe2x80x9cRise ratexe2x80x9d, i.e., the rate at which the gas output from an inflator increases pressure, as measured when such gas output is directed into a closed volume, is a common performance parameter used in the design, selection and evaluation of inflator devices for particular vehicular airbag restraint system installations. It is commonly desired that an inflatable restraint airbag cushion initially inflate in a relatively gradual manner soon followed by the passage of inflation gas into the airbag cushion at a relatively greater or increased pressure rate. An inflator resulting in such inflation characteristics is commonly referred to in the field as producing inflation gas in accordance with an xe2x80x9cSxe2x80x9d curve.
One particularly common type or form of inflator device used in inflatable passive restraint systems is commonly referred to as a pyrotechnic inflator. In such inflator devices, gas used in the inflation of an associated inflatable element is derived from the combustion of a pyrotechnic gas generating material. A variety of combustible pyrotechnic materials have been developed for use in the inflation of automotive inflatable restraint airbag cushions.
Another common form or type of inflator device utilizes or relies on a stored compressed gas. The term xe2x80x9ccompressed gas inflatorxe2x80x9d is commonly used to refer to the various inflators which contain a selected quantity of compressed gas. For example, one particular type of compressed gas inflator, commonly referred to as a xe2x80x9cstored gas inflator,xe2x80x9d simply contains a quantity of a stored compressed gas which is selectively released to inflate an associated airbag cushion.
A second type of compressed gas inflator, commonly referred to as a xe2x80x9chybrid inflator,xe2x80x9d typically supplies or provides inflation gas as a result of a combination of stored compressed gas with the combustion products resulting from the combustion of a gas generating material, e.g., a pyrotechnic.
In the past, compressed gas inflators of various types have commonly been at a disadvantage, as compared to pyrotechnic inflators, in terms of size, weight and/or cost. This is especially significant in view of the general design direction toward relatively small, lightweight and economical modern vehicle components and assemblies. Thus, there is a continuing need and demand for further improved apparatus and techniques for inflating inflatable devices such as inflatable airbag cushions.
At least partially in response to such need and demand, the above-identified related prior U.S. patent application Ser. No. 09/495,975 discloses an improved apparatus for inflating an inflatable device wherein one or more apparatus parameters such as weight, cost, complexity, and size, for example, can desirably be reduced or minimized to a greater extent than otherwise or previously possible or realizable while providing required or desired performance capabilities. This prior patent application discloses an apparatus which includes a first chamber having contents which include at least one gas source material, e.g., nitrous oxide, which upon initiation undergoes dissociation to form dissociation products used to inflate the inflatable device. In accordance with the invention thereof, the apparatus is improved through the inclusion of at least one unreactive dissociation reaction modifier selected from a group consisting of CO2, Xe, SF6 and mixtures thereof. Such at least one unreactive dissociation reaction modifier is stored at least partially in liquefied form in fluid contact with the at least one gas source material in the first chamber. In accordance with a preferred embodiment of the invention, the at least one unreactive dissociation reaction modifier is effective to moderate at least one of the temperature and concentration of the at least one gas source material in the first chamber upon the dissociation of at least a portion of the at least one gas source material.
While such an inflator apparatus can successfully overcome, at least in part, some of the problems associated with prior types of inflator devices, such inflator apparatus and the operation thereof may be subject to certain limitations or complications. For example, operation of such an inflator apparatus having a high concentration of nitrous oxide stored therein, e.g., greater than about 50 molar percent nitrous oxide, can result in the formation of problematic amounts or concentrations of undesirable oxides of nitrogen (NOx), such as NO and NO2. 
As a result, there is a continuing need and demand for further improvements in safety, simplicity, effectiveness, economy and reliability in the apparatus and techniques used for inflating an inflatable device such as an airbag cushion. In particular, there is a need and a demand for an improved inflator apparatus of reduced size and associated methods of operation which also desirably eliminate, avoid or minimize certain problems or complications such as associated with NOx formation.
A general object of the invention is to provide an improved apparatus and corresponding or associated method for inflating an inflatable device.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through an improved apparatus for inflating an inflatable device. The inflation apparatus is of a type wherein a gas generant reactant reacts with oxygen to produce a gaseous inflation medium. The apparatus includes a closed first chamber having contents free of nitrous oxide and which contents include a supply of oxygen. The apparatus also includes an initiator to initiate reaction of at least a fraction of the supply of oxygen with the gas generant reactant to produce a quantity of the gaseous inflation medium. In accordance with a first preferred embodiment of the invention, the apparatus is improved through the inclusion of at least one unreactive reaction modifier selected from a group consisting of CO2, Xe, SF6 and mixtures thereof. In accordance with certain preferred embodiments, such at least one unreactive reaction modifier is desirably stored at least partially in liquefied form in fluid contact with at least a portion of the supply of oxygen in the first chamber.
The prior art generally fails to provide an inflation apparatus and techniques for inflating an inflatable device which desirably reduce or minimize the envelope required thereby to as great an extent as may be desired while, at the same time reducing or minimizing the amounts or concentrations of undesirable oxides of nitrogen (NOx), such as NO and NO2, resulting therefrom.
The invention further comprehends a method for inflating an inflatable safety device in a vehicle. In accordance with one preferred embodiment of the invention, such method includes:
releasing oxygen from a chamber having contents free of nitrous oxide and including a supply of oxygen and a quantity of at least one unreactive reaction modifier selected from a group consisting of CO2, Xe, SF6 and mixtures thereof and reacting a gas generant material with at least a portion of the oxygen from the chamber to produce a quantity of gaseous inflation medium.
In accordance with certain preferred embodiments, at least a portion of the quantity of at least one unreactive reaction modifier is desirably stored at least partially in liquefied form in fluid contact with at least a portion of the supply of oxygen.
xe2x80x9cEquivalence ratioxe2x80x9d (xcfx86) is an expression commonly used in reference to combustion and combustion-related processes. Equivalence ratio is defined as the ratio of the actual fuel to oxidant ratio (F/O)A divided by the stoichiometric fuel to oxidant ratio (F/O)S:
xcfx86=(F/O)A/(F/O)Sxe2x80x83xe2x80x83(1)
(A stoichiometric reaction is a unique reaction defined as one in which all the reactants are consumed and converted to products in their most stable form. For example, in the combustion of a hydrocarbon fuel with oxygen, a stoichiometric reaction is one in which the reactants are entirely consumed and converted to products entirely constituting carbon dioxide (CO2) and water vapor (H2O). Conversely, a reaction involving identical reactants is not stoichiometric if any carbon monoxide (CO) is present in the products because CO may react with O2 to form CO2, which is considered a more stable product than CO.)
For given temperature and pressure conditions, fuel and oxidant mixtures are flammable over only a specific range of equivalence ratios. Mixtures with an equivalence ratio of less than 0.25 are herein considered nonflammable, with the associated reaction being a decomposition reaction or, more specifically, a dissociative reaction, as opposed to a combustion reaction.
As used herein, references to a material as xe2x80x9cunder-oxidized,xe2x80x9d xe2x80x9coxygen-deficientxe2x80x9d or the like are to be understood to refer to a material having an equivalence ratio which is less than one.